This letter describes a fast-settling active rectifier for a 40.68 MHz wireless power transfer receiver for implantable applications. Fast-settling and low power are achieved through a novel direct voltage-domain compensation technique. The rectifier maintains high efficiency during load and link variations required for downlink communication. The system was fabricated in 40nm CMOS and achieves a voltage conversion ratio of 93.9% and a simulated power conversion efficiency of 90.1% in a 0.19 mm² area, resulting in a 118 mW/mm² power density while integrating the resonance and filter capacitors. The worst-case settling of the ON-and OFF-delay compensation in the active rectifier is 200 ns, which is the fastest reported to date.